Compression of fixed word length digital data by Huffman encoding is known as disclosed in an article by D. A. Huffman entitled, "A Method for the Construction of Minimum Redundancy Codes." Proc. IRE, 40: 1098, 1952. Truncated Huffman type encoding also is known as disclosed in an article by U. E. Ruttiman and H. V. Pipberger entitled, "Compression of the ECG by Prediction or Interpolation and Entropy Encoding," IEE Transactions on Biomedical Engineering, Vol. BME-26, No. 11, pp.613-623, Nov. 1979, and an article by K. L. Ripley and J. R. Cox, Jr. entitled, "A Computer System for Capturing Transient Electrocardiographic Data," Pro. Comput. Cardiol. pp. 439-445, 1976. A Huffman code has the property that two or more code words cannot be placed in sequence to generate another member of the code-word set. This property makes it possible to find the beginning and end of each code word when the word length is variable without an end-of-word symbol. The average number of bits per code word is no greater than one plus the entropy of the source.
With a truncated Huffman code, code words are assigned to only a small number of the most probable values of digital data to be encoded. For all other values, the actual digital data is transmitted together with a label.